Conventionally, in JP-A-2003-332562, a break down voltage of a SiC semiconductor device having a Schottky barrier diode (i.e., SBD) is improved. In the device, a micro pipe defect and a small defect disposed in a single crystal substrate made of SiC are filled with an oxide film so that these defects are recovered. Thus, a Schottky electrode does not directly contacts the micro pipe defect and the small defect, so that an electric field intensity is reduced, and a leak current is limited. Thus, the break down voltage of the device is improved.
However, in the above conventional art, even when the micro pipe defect and the small defect are filled with the oxide film, the leak current is not sufficiently reduced. FIG. 7 shows a relationship between a leak current density IR and a Schottky barrier height φb. Specifically, in FIG. 7, a theoretical line is shown, and a white circle in a comparison device and a black circle in the above device are also shown. The white circle represents a case where the micro pipe defect and the small defect are not filled with the oxide film, and the black circle represents a case where the micro pipe defect and the small defect are filled with the oxide film. The leak current density of the above device, i.e., the black circle is reduced, compared with the leak current density of the comparison device, i.e., the white circle. However, the leak current density is not sufficiently reduced in the above device. Thus, it is possible to reduce the leak current density so as to reach the theoretical line. Accordingly, it is required to improve the leak current much more so as to reach the theoretical line.
Here, as shown in FIG. 7, when the Schottky barrier height φb is small, the leak current density IR becomes large. Thus, the relationship between the Schottky barrier height φb and the leak current density IR is a trade off relationship. Accordingly, it is difficult to reduce both of the Schottky barrier height φb and the leak current density IR. However, it is required to approach the relationship to the theoretical line.